The present invention relates to a wafer holding device in a surface inspection system to be used in an inspecting process for manufacture of semiconductor products.
A semiconductor product is manufactured by forming a large number of semiconductor devices on a wafer. Because of the requirements on high density and high integration, increasingly finer fabrication is needed. Further, for the purpose of improving the production yield, a wafer with an increasingly larger diameter is now being produced.
With the progress of high density, high integration and finer production, particles attached on the wafer exert extensive influence on the product quality and the production yield. For this reason, the inspecting process is incorporated in the manufacturing process of semiconductor products. A surface inspection of the wafer is performed by using an inspection system, and attaching condition of the particles on the wafer and damage of the wafer are inspected.
In the surface inspection for the wafer, the wafer is rotated at high speed. A laser beam is irradiated to the wafer surface and is scanned in a circumferential direction. The laser beam reflected from the wafer surface is received, and the attachment of the particles, etc. is detected by examining the reflecting condition.
As described above, the wafer is now being produced with increasingly larger diameter. Further, there are demands to improve the throughput and to improve the productivity, and wafer rotating speed during the inspecting is also increased. Therefore, during the inspecting of the wafer, high centrifugal force is applied on the wafer held in the device.
In this respect, a wafer holding device must reliably hold the wafer even at high-speed rotation under high centrifugal force applied.
Description will be given below on a conventional type wafer holding device referring to FIG. 18 and FIG. 19.
A wafer chuck 1 is provided on an upper end of a rotation shaft (not shown).
The wafer chuck 1 comprises a shaft 2 connected to the rotation shaft and a vacuum suction unit 3 in a disk-like shape. A number of circumferential grooves 4 are formed coaxially on an upper surface of the vacuum suction unit 3. A radial groove 5 is formed in a radial direction, and the circumferential grooves 4 are communicated with the radial groove 5. The shaft 2 is designed with a hollow portion 6, and it is communicated with a vacuum pumping equipment (not shown) via the hollow portion 6.
When the wafer 7 is chucked, the wafer 7 is received so that the wafer 7 is coaxially aligned on the vacuum suction unit 3. The wafer 7 has a diameter larger than the diameter of the vacuum suction unit 3, and the peripheral portion is protruded. When the wafer 7 is received, each of the circumferential groove 4 and the radial groove 5 is turned to a closed space. By performing vacuum pumping through the hollow portion 6, the inner spaces of the circumferential groove 4 and the radial groove 5 are turned to negative pressure. By the pressure difference from outside, the wafer 7 is sucked and held by the vacuum suction unit 3.
However, in the conventional wafer holding device, as shown in FIG. 20, when the wafer 7 is sucked by the vacuum suction unit 3, the wafer 7 is supported by convex portions 8 in arcuate shapes between the circumferential grooves 4, and the external pressure is applied on the entire surface of the wafer 7. As a result, delicate and complicated flexion occurs between the convex portions 8 and 8. Also, the portion protruding from the vacuum suction unit 3 is bent downward by its one weight. In case the election is irregular, a direction of the laser beam reflected from the surface of the wafer 7 is changed irregularly. From the laser beam reflected from the normal surface, particles and surface abnormality are erroneously detected. This may cause erroneous measurement.
The convex portions 8 are brought into contact with an entire rear surface of the wafer 7, and high contact pressure is applied on the contact portion. This may lead to generation of damage and also to the possibility that foreign objects may be attached on the rear surface of the wafer 7.
Also, close contact between the wafer 7 and the convex portions 8 exerts strong influence on adsorption of the wafer 7. When foreign objects are attached on a contact surface of the convex portion 8, adsorption is decreased. As a result, the wafer 7 may not be aligned with the center of the vacuum suction unit 3 due to angular acceleration at the initiation of rotation or at the stopping of the vacuum suction unit 3. When the wafer 7 is rotated at high speed, high centrifugal force is applied on the wafer. When the wafer 7 is not aligned well with the vacuum suction unit 3 or the center of the wafer 7 is deviated at the time of attaching, the wafer 7 may be detached from the vacuum suction unit 3.
It is an object of the present invention to provide a wafer holding device, by which it is possible to reliably hold a wafer even during high-speed rotation and to prevent the development of complicated flexion on the surface of the wafer when the wafer is held in the device.
To attain the above object, the wafer holding device according to the present invention comprises a rotating baseplate, a wafer seat which is provided on the rotating baseplate coaxially with the rotating baseplate and which receives a peripheral edge of a wafer by a circumference, a predetermined number of chuck levers rotatably mounted on the wafer seat so that the chuck levers can be rotated around an axis extending in a tangential direction on a circumference of the rotating baseplate, and springs for resiliently pushing an end of the chuck lever toward the wafer seat, wherein the peripheral edge of the wafer received on the wafer seat is pinched by the wafer seat and the chuck lever. Also, the present invention provides the wafer holding device as described above, wherein a wafer receiving surface of the wafer seat has a downslope gradient toward a center of the rotating baseplate, and a wafer abutting surface of the chuck lever has an upslope gradient toward the center. Further, the present invention provides the wafer holding device as described above, wherein the chuck lever is extended above and under the rotating baseplate, an outer end of a chuck shaft slidably provided in a radial direction is engaged with a lower end of the chuck lever, an inner end of the chuck shaft is engaged with a chuck disk provided coaxially with the rotating baseplate, the chuck shaft is displaced in the radial direction by rotation of the chuck disk, and the chuck lever is rotated. Also, the present invention provides the wafer holding device as described above, wherein centrifugal force applied on a lower half of the chuck lever is designed to be bigger than centrifugal force applied on an upper half of the chuck lever. Further, the present invention provides the wafer holding device as described above, wherein the wafer seat has at least three notches, and there is provided a delivery pin which is positioned on each of the notches, which is movable in a vertical direction on the same circumference as the wafer seat, and which receives the wafer above the wafer seat. Also, the present invention provides the wafer holding device as described above, wherein the device comprises a cylinder cam rotatably mounted with respect to the delivery pin, a chuck disk rotatably provided coaxially with the rotating baseplate, and a link bar for connecting the chuck disk with the cylinder cam, wherein the cylinder cam is rotated via the link bar by rotation of the chuck disk, and the delivery pin is moved up or down by rotation of the cylinder cam.